1. Field of the Invention
This invention relates generally to pipe fittings and more particularly to a standard sized fitting having a simplified construction for interconnecting concentric pipes together to a gas meter riser unit.
2. Description of the Prior Art
There are in existence today numerous assemblies of components which form pipe joints or couplings for use in pipe assemblies known as anodeless risers. A review of such assemblies reveals relatively complex and concomitant costly assembly configurations. Accordingly, a need has arisen for a simplified transition pipe fitting which reduces the costs of manufacture and production. Such need is accentuated by government regulations which require each natural gas meter to be electrically insulated from adjacent building piping and which require all below ground metal parts of natural gas service lines to be protected against corrosion. Where plastic pipe is used as an underground service line for natural gas, the above ground portion of such line must be protected against deterioration and external damage. Furthermore, such service lines are not to be used for the support of external loads. In addition, service lines inside a building must be protected against external damage, and must be generally insulated against stray electrical currents from the building piping.
U.S. Pat. No. 4,284,297 to Godkin, U.S. Pat. No. 4,094,537 to Lyall, U.S. Pat. No. 4,094,536 to Cole et al and U.S. Pat. No. 3,861,719 to Hand each disclose a meter riser assembly generally directed to the above-mentioned needs, however, such assemblies clearly disclose relatively complicated structures. U.S. Pat. No. 2,087,920 to Maschuch, U.S. Pat. No. 2,025,382 to Fletcher et al, U.S. Pat. No. 1,620,692 to Rigney and U.S. Pat. No. 918,843 to Glidden each disclose a union type fitting wherein one of the main assembly union elements is formed to receive a packing element or seal having a substantially trapozoidal or frustoconical cross section, however, such references disclose only a single packing element or seal and therefore do not provide a back-up or safety seal.
U.S. Pat. No. 3,337,181 to Winnerstrom discloses a pipe fitting including a section having an annular channel formed therein for receiving an O-ring for effecting a single fluid tight seal. Finally, U.S. Pat. No. 3,576,335 to Kowal et al discloses an annular member secured to an end portion of a tube by brazing. Such annular member supports and retains the tube end within the fitting against axial withdrawal.
Thus, there exists a need for a simplified, inexpensive transition pipe fitting which provides at least two gas tight seals and which resists pull out of an inner tube from the point of connection with an outer tube.